1. Field of the Invention
This invention includes the apparatus and method for detecting facsimile transmission (CNG) signals on a telephone line while answering a call waiting (CW) signal. It is more specifically directed to a CNG detection and switching apparatus for use during a call waiting sequence when the telephone line is in use receiving data.
2. Discussion of the Background
Current line sharing devices have Calling Tone Signal (CNG) detection that allows the device to direct an incoming call to a facsimile machine. In addition, other detectors are capable of detecting coded Dual Tone Multi-Frequency (DTMF) operation or function signals as well as diverting and switching the incoming telephone call to a computer modem or other devices. In this way data can be received over a telephone line either by facsimile, computer modem, or other telephony devices.
The device that is most common for this type of switching is called a voice/data switch. The incoming telephone line is connected to the voice/data switch and a number of selected accessories such as a telephone set, answering machine, facsimile machine, computer modem, etc. are connected to assigned ports provided on the device. A microprocessor is utilized in the switch circuitry to provide automatic switching of the incoming telephone line to the proper port by the use of the incoming operation or function identification signals. These signals include the CNG signal as well as the coded DTMF signals that have been established as standards for the initialization of the various accessory equipment. At the present time, the CNG signal associated with facsimile machines is a 1100 Hertz tone. Various other tones have been established in connection with telephone systems for performing various functions and operations, such as a 440 Hertz tone for the call waiting function.
As stated above, the voice/data switch normally is automatic but it also can be used manually by pre-programming through a telephone key pad various DTMF tone codes which direct the device to perform certain operations and to make the required switch to the various desired ports.
One of the major problems that has been encountered in the past has been the inability to use the incoming telephone line while connected to a data receiving device, such as a computer modem. During the time that the telephone line is directly connected to the computer modem the line is “off-hook” and occupied and therefore “busy” to any other type of utilization. However, the telephone system providers have incorporated a service in this system which allows an incoming call waiting (CW) signal to be superimposed or inserted on the busy or occupied telephone line. Also, an additional service has been added which allows the caller ID (CID) signal to be sent after the call waiting signal to identify the new or second caller. In this way, the user of the “busy” telephone line is informed as to the identity of the caller and thus can make a decision as to whether to interrupt the present operation or to continue the present operation and ignore the incoming call.
One of the major deficiencies which has been uncovered through operations of this type is when the line is “busy” transmitting and receiving data the call waiting (CW) signal is not recognized and no “hook flash” is performed to make a telephone switch connection to a second caller. In addition, there has been no provision in the past for the detection of any coded function signals for a data transmission call during the call waiting sequence which could in turn automatically switch the device to a data outlet port to which a designated telephone accessory such as a fax machine is connected. The present invention is directed to this deficiency and provides a method and an apparatus for selectively detecting these signals and making the necessary new switch connections as a response.
In the past, it has been known to provide a CNG or DTMF signal detector which continuously monitors the telephone line but of course this is subject to numerous false detections due to the presence of analog and digital signals on the telephone line while it is in use. Further, as described above, when a computer modem is connected and using the telephone line, the user has no way of identifying that a call waiting tone signal has been received. Some home offices and businesses have separate dedicated telephone lines for the facsimile machine and the computer modem which eliminates this problem but this is a very expensive alternative. The present invention allows a sequenced detection of a CNG signal on a second incoming call that has been triggered by the call waiting signal while a computer modem or other data receiving device is in use.